'Why can't I be judged for who I am now, not what I was then?" asks the novelist Anne Perry. But she knows the question is pointless. Sometimes the past casts too long a shadow. In 1954, Perry - then a 15-year-old called Juliet Hulme, living in New Zealand - helped to bludgeon to death the mother of her friend, Pauline Parker. Both were convicted of murder and sent to prison. The grisly story was the subject of Peter Jackson's film Heavenly Creatures, in which Hulme was played by Kate Winslet. She was released from prison in 1959 and set about reconstructing her life. "I had to give up my past - the hardest thing imaginable - and begin life in my new identity as Anne Perry, knowing even a tiny slip could unravel everything," she says. She became a Mormon and moved to a small, secluded community in Scotland.
In the past four decades, Perry has published 40 books and established herself as a leading crime novelist, selling more than 10m copies. Her new novel, No Graves As Yet, is the first of a five-part series centred on the first world war. When it appeared in the US, it topped the New York Times bestseller list.
Perry's books grapple with questions of sin and repentence, the price of redemption and forgiveness. "It is vital for me to go on exploring moral matters," she says. This series - more literary and epic in scope than her pacy earlier novels - will look at personal morality "against the background of that five years of war when things were so changed for men and women. I wanted to explore what people will do when faced with experiences and inner conflicts that test them to the limit."
In 1954, Hulme felt as if she had been pushed to the limit. Three days before she took part in the killing of Honora Parker on June 22, her parents announced that they were to divorce - triggered by Hulme having found her mother, Hilda, in bed with a lover. At the same time, her father lost his job and she was to be sent to South Africa to stay with an aunt. The shock to Hulme - who had not been at school because of tuberculosis, from which she had suffered since the age of 13 - was cataclysmic.
She turned to her close friend, Parker, a working-class girl from a humble background. Some felt it was a curious friendship for Hulme, whose family were well to do, her mother glamorous and clever. The two friends believed they could stay together if Pauline's mother would let her leave New Zealand. Her refusal triggered Parker's murderous rage and Hulme believed she owed it to her friend to help lure Mrs Parker to a Christchurch park and cosh her with a brick in a stocking.
"I felt I had a debt to repay," says Perry. "Pauline was the only one who had written to me when I was in hospital, and she threatened to kill herself if I didn't help. She was vomiting after every meal and losing weight all the time. I am sure now she was bulimic. I really believed she would take her life and I couldn't face it."
Hulme served five years at Mt Eden women's prison in Auckland - "supposedly the toughest in the southern hemisphere," she says with what sounds like pride. She was the only child in the prison, and was kept in solitary confinement for three months in a tiny cell. "It was cold, there were rats, canvas sheets and calico underwear. I had to wash out my sanitary towels by hand and they put me on to physical labour until I passed out."
Yet Perry now calls her time in prison "the best thing that could have happened". "It was there that I went down on my knees and repented," she says. "That is how I survived my time while others cracked up. I seemed to be the only one saying, I am guilty and I am where I should be."
For more than 30 years after her release, Perry lived quietly in Scotland. Then, in 1994, she got a call from her agent telling her that a film of her story was to be released and that a journalist in New Zealand had revealed her identity. "It seemed so unfair," she says. "Everything I had worked to achieve as a decent member of society was threatened. And once again my life was being interpreted by someone else. It had happened in court when, as a minor, I wasn't allowed to speak and I heard all these lies being told. And now there was a film, but nobody had bothered to talk to me. I knew nothing about it until the day before release. All I could think of was that my life would fall apart and that it might kill my mother."
Her mother survived and is still alive, aged 92, but there was much prurient interest in the case - great play was made of an alleged lesbian relationship between the two girls. Reporters camped out in her mother's garden and phoned Perry in the middle of the night.
Perry asked a senior figure in the Mormon church if her membership would be affected. "He said 'your calling comes from God and He knows'," Perry recalls. "He also told me I would not lose a single friend over it. It didn't seem possible, but I have learned how decent and compassionate people can be. Not a single friend has gone. That surprised the hell out of me."
· No Graves As Yet is published by Headline, priced £14.99.